KIMBERLY DOZIER

This March 25, 2007, file image, made from video posted on a website frequented by Islamist militants and provided via the IntelCenter, shows al-Qaida militant Abu Yahia al-Libi. A CIA drone strike Monday, June 4, 2012, targeted al-Qaida's second in command, Abu Yahia al-Libi, in Pakistan, but it was unclear whether he was among those hit, U.S. officials said. U.S. officials say fewer than five people were hit, although Pakistani officials say more than a dozen people were killed in two days of strikes in Pakistan. (AP Photo/IntelCenter, File)

WASHINGTON - A U.S. official says a drone strike in Pakistan's northwest tribal region has killed al-Qaida's second-in-command.

The death of Abu Yahya al-Libi is a significant blow to the terror network, which has lost a string of top leaders at the hands of the American drone program.

The official, who spoke on condition of anonymity to discuss intelligence matters, says that no one left in al-Qaida comes close to replacing the expertise al-Qaida has just lost.

Al-Libi would be the latest in the dozen-plus senior commanders removed in the clandestine U.S. war against al-Qaida since Navy SEALs killed Osama bin Laden just over a year ago. Al-Libi, a hero in militant circles for his 2005 escape from an American military prison in Afghanistan, was elevated to al-Qaida's No. 2 spot when Ayman al-Zawahri rose to replace the slain bin Laden.